There's an interesting article on the front page of the WMAS homepage.  Here it is:  http://pubs.acs.org/cen/news/8233/8233notw7.html - http://pubs.acs.org/cen/news/8233/8233notw7.html  

What researchers found was that Montastraea cavernosa coral contain sybiotic cyano bacteria (in addition to the common symbiotic dinoflagellates).  Cyano has the ability to "fix" disolved nitrogen gas in the water into organic nitrogen compounds (ammonia/nitrate) which corals then can use.  That's a very interesting discovery!  It means that, at least in M. cavernosa, corals are not dependent soley upon nutrient poor waters around reefs for their nitrogen demand.